Optimal microbubble production rate from a flow-focusing microfluidic device as a function of nozzle size, gas pressure, and liquid flow rate

Previous studies have shown that flow-focusing microfluidic devices (FFMDs) produce monodisperse microbubbles with tunable diameters in a continuous process and that microbubble diameter is a function of gas and liquid flow rate. However, there is currently no model for microbubble production rate from an FFMD. In this paper, PDMS-based, rectangular-nozzle FFMDs are characterized in order to determine parameters and a model for optimal microbubble production - high production rate while maintaining monodispersity. Parameters tested include nozzle width, liquid phase concentration, gas pressure, and liquid flow rate. Microbubble diameter and production rates were determined optically using a high speed camera. The data was fit in order to determine an empirical model for microbubble diameter and highest production rate as a function of FFMD parameters. We encountered a quadratic relationship between production rate and diameter and a linear relationship between pressure and microbubble diameter sensitivity to gas and liquid flow rate.